1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to methods for performing a wet clean of a surface having an exposed silicon/silica interface, which wet clean is useful in the manufacture of semiconductor devices. The methods are particularly useful for a post chemical mechanical polishing clean of a surface having an exposed silicon/silica interface.
2. The Relevant Technology
Chemical mechanical polishing is finding increasing application in the manufacture of semiconductor devices to planarize surfaces in preparation for high resolution photolithography and for other purposes. Chemical mechanical polishing involves polishing an uppermost film on the surface of a semiconductor wafer by use of a polishing pad and a polishing slurry. The slurry contains polishing particles. Pad types and slurry compositions vary depending on the material being polished and other factors.
Chemical mechanical polishing is particularly useful where feature sizes of less than 0.5 micron must be defined over a topography already existing on the wafer surface. In such circumstances, a reflowed silica glass layer is insufficiently planar, but with chemical mechanical polishing, sufficient planarity may be achieved to facilitate high resolution photolithography. Chemical mechanical polishing may also be employed to completely remove portions of a layer being polished, so that underlying material is exposed. In either case, a clean step is required after the chemical mechanical polishing to clean polishing slurry from the wafer surface.
Where silica (silicon dioxide) or silicon is the layer being polished, the polishing slurry typically contains silica particles having an average size of about 30 nanometers (nm). The silica particles that remain on a silica surface after polishing are typically removed by a clean process including an HF (hydrofluoric acid solution) dip followed by a deionized water rinse. Silica particles and other contamination remaining on a silicon surface after polishing are typically cleaned in an ammonium hydroxide solution or the like.
Where a silica layer is polished until some silicon is exposed, or where a silicon layer is polished until some silica is exposed, the above typical clean processes can result in problems. While the typical clean process for silica is effective to remove silica particles from a silica surface, a silicon surface is not adequately cleaned. Silica particles tend to collect on the silicon surface and, once the clean process is complete, tend to permanently adhere there, regardless of further cleans. The typical clean processes for silicon are likewise ineffective to remove silica particles from a silica surface. Further, an ammonium hydroxide clean, which etches silicon, can be unacceptable where particularly fine or small silicon structure must be preserved. Accordingly, there exists a need for a clean process which can remove silica particles from both silica and silicon surfaces, and particularly without etching the silicon surface.